Among thermoplastic resins, polyolefin resin enables light weight and good cost efficiency and is excellent in moldability, chemical resistance, and mechanical strength, and thus it is used for various applications as film, fiber, and molding material.
However, since polyolefin resin has low polarity and small intermolecular force, it has problems in that coating property, adhesive property to and compatibility with polar material, and scratch resistance are inferior.
To solve these problems, a lot of copolymer compositions in which a vinyl monomer having an acid is generally grafted are proposed.
For example, to improve adhesive property of polyolefin resin, a graft copolymer in which a vinyl polymer segment formed from a vinyl monomer having carboxylic acid is directly bonded to polypropylene resin segment is proposed (see Patent Document 1: Japanese Patent No. 2885919, page 2 to 3).
Further, to improve adhesive property and scratch resistance of thermoplastic elastomer, proposed is a method of blending a graft copolymer with thermoplastic elastomer, the graft copolymer in which a vinyl polymer segment formed from a vinyl monomer having carboxylic acid is directly bonded to ethylene•α-olefin copolymerized rubber segment (see Patent Document 2: Japanese Patent Publication No. 2-51455 (page 3)).
However, in the graft copolymer disclosed in Patent Documents 1 and 2, since the vinyl copolymer segment formed from a vinyl monomer having carboxylic acid is directly bonded to polypropylene resin or ethylene•α-olefin copolymerized rubber, the improvement effects on adhesive property and scratch resistance are not sufficient and further improvements have been expected.
Furthermore, the graft copolymers disclosed in these documents are produced by a method in which the vinyl monomer is directly reacted through grafting with the polyolefin resin using a polymerization initiator, and thus they have some problems in that the reactivity during graft reaction is low and side reaction such as disintegration or crosslinking of polyolefin resin occurs during the reaction. It is thus considered that a graft copolymer having excellent properties is hard to be obtained by these methods.